Method of sintering titanium and like metals



Patented Mar. 27, 1951 METHOD OF SINTEBING TITANIUM AND LIKE METALS Douglas W. Rostron, Toronto, Ontario, Canada,

assignor to Dominion Magnesium Limited, Toronto, Ontario, Canada, a corporation of Ontario No Drawing. Application December 13, 1948, Se-

rial No. 65,079. In Canada November 4, 1948 2 Claims.

This invention relates to a method of sintering bars, compacts or the like of metals which react with oxygen, nitrogen, hydrogen and the like at temperatures incident to sintering treatment and mor particularly to the treatment of titanium.

When sintering such reactive metals at temperatures above say 800 C. they tend to react with oxygen, nitrogen and like gases surrounding them to form stable compounds which go into solid solution in the metal, imparting thereto undesirable physical properties. Heretofore the practice has been to sinter the compacts, briquettes or bars in a vacuum sufliciently high to prevent such contamination. It is difi'icult and expensive to maintain eifectively the required vacuum conditions in commercial operation.

In accordance with the present invention the metal bars, compacts or briquettes of titanium are sintered in the presence of an alkaline earth metal which is more reactive to the contaminating gases than the metal under treatment. Calcium is preferred but magnesium, lithium, strontium and barium may be used. The compacts may be sintered while submerged in molten calcium or other alkaline earth metal or they may be sintered in an atmosphere of such metal in vapour form. Argon or other inert gas may be combined with the vapour of the alkaline earth metal to provide the protective sintering atmos phere.

The following specific examples are illustrative of the operation of the invention.

Titanium powder is pressed into compact or briquette form, by usual powder metallurgy methods, for sintering. Lubricants should not be used during the pressing operation.

When sintering in molten metalthe compacts and calcium metal are placed in a container of mild steel. The container is closed and placed in the upper cool zone of a sinteringfurnace. The furnace, is closed, evacuated and filled with argon to a pressure in excess of atmospheric and the container is lowered into the hot zone of the furnace maintained at about 1000 C. When sintering is complete the container is raised into the cool zone of the furnace where the metal is allowed to 0001 before it is removed from the furtrace and container. The sintering treatment rendersthe compressed mass Of metal powder practically solid and in this form the tendency to react with contaminating gases is substantially eliminated. Even if the sintered compact is exposed to the air at relatively high temperature the contamination is superficial. Thus the sintered compact may be readily cooled sufliciently before exposure to the atmosphere. Alternatively the compacts may be placed in a mild steel basket and lowered into a bath of molten calcium under a protective covering of argon. When sintering is complete the basket is raised allowing the molten calcium to drain back into the bath.

When sintering in vapour of calcium the container carrying the compacts is suspended above the bath of molten calcium during the heat treatment above described. In this procedure it is necessary to use only sufficient calcium to saturate the atmosphere within the furnace.

Any of the protecting alkaline earth metal adhering to the sintered compacts may be readily removed by treatment with dilute hydrochloric acid. When sintered in calcium vapour very little of the protecting metal adheres to the compacts.

The time and temperature required for sintering in this manner are substantially the same as used in the usual high vacuum sintering procedure. However, the method is more economical than the high vacuum method and because the calcium completely eliminates reaction of the metal being sintered with oxygen, nitrogen and the like, the physical properties of the sintered metal are improved.

Other metals like sodium, cadmium and lead have been tried but they have been found relatively ineifective and unsuitable for sintering titanium which is particularly reactive to oxygen and nitrogen. The alkaline earth metals, and particularly calcium, have been found to have a greater afiinity for the reacting gases than titanium.

While the invention has been described with particular reference to titanium, it is equally applicable to other reactive metals like zirconium, vanadium, hafnium and chromium.

What I claim is:

1. A method of treating titanium and like reactive metal powder which comprises compressing the powder into compacts, placing the compacts and a mass of alkaline earth metal in a closed zone, evacuating air and filling the closed zone with an inert gas, heating to render the alkaline earth metal fluid to intimately surround the compacts and while maintaining the compacts completely surrounded with the fluid alkaline earth further heating at a temperature of about 1000 C. to sinter the powder and render the compacts solid and resistant to oxidation.

2. A method as defined in claim 1 wherein the compacts are immersed in a bath of molten calcium while heating to sinter the compacted UNITED STATES PATENTS powder- Number Name Date DOUGLAS ROSTRON- 1519,975 H Gero July 9, 1929 2,206,395 Gertler July 2, 1940 REFERENCES CITED 5 2,352,246 Benner eta June 27, 1944 The following references are of record in the file of this patent: OTHER REFERENCES Jones: Powder Metallurgy; published by Edward Arnold. & 00., London, 1937, page 49. 

1. A METHOD OF TREATING TITANIUM AND LIKE REACTIVE METAL POWDER WHICH COMPRISES COMPRESSING THE POWDER INTO COMPACTS, PLACING THE COMPACTS AND A MASS OF ALKALINE EARTH METAL IN A CLOSED ZONE, EVACUATING AIR AND FILLING THE CLOSED ZONE WITH AN INERT GAS, HEATING TO RENDER THE ALKALINE EARTH MEATL FLUID TO INTIMATELY SURROUND THE COMPACTS AND WHILE MAINTAINING THE COMPACTS COMPLETELY SURROUNDED WITH THE FLUID ALKALINE EARTH FURTHER HEATING AT A TEMPERATURE OF ABOUT 1000* C. TO SINTER THE POWDER AND RENDER THE COMPACTS SOLID AND RESISTANT TO OXIDATION. 